An investigation has been launched after a young black man died in a shop after being chased by police.
The 20-year-old, named locally as Rashan Charles, became ill shortly after his arrest.
A police spokesman said he was seen "trying to swallow an object" after he was pursued and a police officer "sought to prevent the man from harming himself".
CCTV video has emerged apparently showing the incident in which an officer is seen grappling with Mr Charles on the floor.
Mr Charles became ill shortly after he was detained in Kingsland Road, Hackney, at 1.45am on Saturday morning.
He was later pronounced dead in hospital.
An investigation has been opened by the Independent Police Complaints Commission (IPCC) - as is standard with all deaths in police custody.
It said it had obtained evidence "which indicates an object was removed from his throat at the scene".
Simon Lawrence, the borough commander for Hackney, said he recognised there would be "speculation" over the circumstances of Mr Charles' death.
"Our thoughts remain with his family and friends," he said.
"The Independent Police Complaints Commission (IPCC) has launched an independent investigation to establish what happened and has viewed the officers' body worn video.
"There is likely to be speculation over the next few days regarding what led to this man becoming ill, so I would encourage people to keep up-to-date with the IPCC's statements, as and when they are released.
"All police officers are fully aware that they will be asked to account for their actions - officers are not exempt from the law and we would not wish to be."